The lifting capacity of an average person amounts to not more than a few hundred pounds. For this reason, people have turned for centuries to mechanical means of lifting heavy items. Some of the means devised include pulley systems, cranes, scissor lifts, or linear actuators. One type of linear actuator of particular interest here is a rack and pinion device.
Rack and pinion devices are configured to convert rotational motion to linear motion. They are often used for creating horizontal linear motion, such as in transport, packaging, and assembly machines, but rack and pinion devices can also be used for vertical linear motion. However, when lifting heavy items vertically, rack and pinion devices have some disadvantages. First, rack and pinion devices normally have only a few points of contact between the rack and the pinion. If a rack and a pinion have contact at only a few points, those points of contact may be put under disproportionate amounts of stress when lifting, which could cause the rack and pinion device to fail. In contraptions in which reliability or safety are significant concerns, such as in an elevator, taking chances with parts that might break under load could lead to disastrous results. This problem is sometimes solved by increasing the size and, therefore, the load capacity of the rack and pinion, but larger parts are harder to manufacture, require more space, cost more, and might require larger motors, all of which lead to decreased efficiency, which is especially undesirable if trying to create a green or sustainable product. One further issue with rack and pinion devices is that these devices generally are not placed in corners. That is because the motor extending out from the pinion is generally too large to fit in the space available within the angle of the corner. This limits the versatility of the devices.
In light of the foregoing, what is needed is a rack and pinion device in which the number of points of contact between the rack and pinion is increased. Also, a device is needed in which the motor can be distanced from the rack, so that the devices can be placed in corners. This could conceivably be accomplished through the use of a silent chain in place of a pinion. Silent chains, like pinions, are generally built for rotational motion. However, if the rotational motion of a silent chain could be converted to linear motion, because of the length of a silent chain, numerous points of contact between a silent chain and a rack could be established, rather than the few points of contact established between a pinion and a rack. In addition, a silent chain would allow a motor to be distanced from the rack, as far away as the length of the silent chain would allow. This would enable racks to be placed and utilized in corners. Unfortunately, the profile of a typical silent chain is built to engage only with a sprocket, not with a rack. Therefore, a silent chain with a profile that would allow it to engage with both a circular sprocket and a linear rack is needed. Finally, a rack that can be placed in corners is needed as well.